Remove return bool in SurfaceOzoneEGL::OnSwapBuffersAsync

ui/ozone/platform/drm/gpu/gbm_surfaceless.cc

Index: ui/ozone/platform/drm/gpu/gbm_surfaceless.cc
diff --git a/ui/ozone/platform/drm/gpu/gbm_surfaceless.cc b/ui/ozone/platform/drm/gpu/gbm_surfaceless.cc
index 6b110e9bd18a6ef65df1d7c8a4e6f28b4a38ccb8..737a0664a6882d79458434c46a815c1e496c2275 100644
--- a/ui/ozone/platform/drm/gpu/gbm_surfaceless.cc
+++ b/ui/ozone/platform/drm/gpu/gbm_surfaceless.cc
@@ -40,11 +40,10 @@ bool GbmSurfaceless::OnSwapBuffers() {
   return false;
 }
 
-bool GbmSurfaceless::OnSwapBuffersAsync(
+void GbmSurfaceless::OnSwapBuffersAsync(
     const SwapCompletionCallback& callback) {
   window_->SchedulePageFlip(planes_, callback);
   planes_.clear();
-  return true;
 }
 
 scoped_ptr<gfx::VSyncProvider> GbmSurfaceless::CreateVSyncProvider() {